1. Field of the Invention
The present invention relates to an electrode assembly, a cathode device and a plating apparatus that may be employed in an ideal manner when plating substrates for various types of electronic components, IC wafers or the like.
2. Discussion of Background
During a plating process for substrates for various types of electronic components and IC wafers and the like, plating must be implemented within a limited planar area on the object that is being plated, i.e., the substrate or wafer. In order to implement a plating process, a plating base film is formed in advance on a surface of the object to be plated and then plating is implemented by placing a cathode device in surface contact with the plating base film in such a manner that the cathode device surrounds the plating area. Publications that disclose this prior art technology include Japanese Unexamined Patent Publication No. 66698/1992 and Japanese Unexamined Patent Publication No. 125596/1993. In the cathode devices of the known art disclosed in these publications, a cathode is placed in surface contact with the object being plated.
Methods that may be adopted to plate an object to be plated such as a wafer include the frame plating method and the pattern plating method. In the frame plating method, a resist frame is formed in advance on the wafer by employing a high-precision pattern forming technology such as photolithography and the required plate is electro-deposited within an area that is not covered by the resist frame.
In the pattern plating method, almost the entire surface of the plate forming surface of the object to be plated is covered with a resist film, a pattern of perforations for plating is opened in the resist film and the plate is electro-deposited at the area where the pattern of perforations is present.
Cathode devices employed in the frame plating method and the pattern plating method bear similarity in that they are provided with a cathode member that comes in contact with the plating base film deposited at a front surface of the object to be plated, although their structural characteristics are somewhat different otherwise. The cathode member is provided with a frame portion that comes in contact with the object to be plated and a hole through which the plating bath solution enters. The internal circumferential edge of the frame portion that defines the hole is exposed.
One of the problems of the cathode device in the prior art described above is caused by the exposure of the internal circumferential edge of the cathode member that comes into contact with the plating base film. When the internal circumferential edge of the cathode member is exposed, the plating film becomes deposited in a continuous manner between the plating base film and the internal circumferential edge of the cathode member. If the plating film becomes deposited in this manner, the plating film and the plating base film deposited on the object to be plated will peel off at the contact area where they are in contact with the cathode member when the object to be plated is removed from the cathode device after the plating process is completed in the frame plating method.
In the pattern plating method, the plating film will become adhered to the internal circumferential edge of the cathode member, causing a change in the diameter of the hole at the cathode member, and thus, when continuous plating is implemented using a single cathode device to plate different wafers, the film formation rate of the plating film among the individual wafers becomes unstable, which results in poor repeating reproducibility among the wafers.